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TwitterDOI: 10.1051/0004-6361/200912055
A possible architecture of the planetary system HR 8799
M. Reidemeister, A. V. Krivov, T. O. B. Schmidt, S. Fiedler, S. Müller, T. Löhne, and R. NeuhäuserAstrophysikalisches Institut und Universitätssternwarte, Friedrich-Schiller-Universität Jena, Schillergäßchen 2–3, 07745 Jena, Germany
e-mail: krivov@astro.uni-jena.de
Received 12 March 2009 / Accepted 20 May 2009
Abstract
HR 8799 is a nearby A-type star with a debris disk and three planetary
candidates, which have been imaged directly. We undertake a coherent analysis of
various observational data for all known components of the system, including the
central star, imaged companions, and dust. Our goal is to elucidate the
architecture and evolutionary status of the system. We try to further constrain
the age and orientation of the system, the orbits and masses of the companions,
and the location of dust. On the basis of the high luminosity of debris dust and
dynamical constraints, we argue for a rather young system's age of 
50 Myr.
The system must be seen nearly, but not exactly, pole-on. Our analysis of the
stellar rotational velocity yields an inclination of 13–30°,
whereas i 
20° is needed for the system to be dynamically stable,
which suggests a probable inclination range of 20–30°. The
spectral energy distribution, including the Spitzer/IRS spectrum in the
mid-infrared as well as IRAS, ISO, JCMT, and IRAM observations, is naturally
reproduced by two dust rings associated with two planetesimal belts. The inner
“asteroid belt” is located at ~10 AU inside the orbit of the innermost
companion and a “Kuiper belt” at 100 AU is just exterior to the orbit of
the outermost companion. The dust masses in the inner and outer ring are
estimated to be 
1 
10-5 and 4 10-2 Earth masses,
respectively. We show that all three planetary candidates may be stable in the
mass range suggested in the discovery paper by Marois et al. (2008) (between 5 and
13 Jupiter masses), but only for some of all possible orientations. For
(Mb,
Mc,
Md) = (5, 7, 7) Jupiter masses, an inclination i 20° is
required and the line of nodes of the system's symmetry plane on the sky must
lie within between 0° an 50° from north eastward. For higher
masses
Mb,
Mc,
Md from
(7, 10, 10) to
(11, 13, 13), the constraints on both
angles are even more stringent. Stable orbits imply a double (4:2:1) mean-motion
resonance between all three companions. We finally show that in the cases where
the companions themselves are orbitally stable, the dust-producing planetesimal
belts are also stable against planetary perturbations.
Key words: planetary systems: formation -- circumstellar matter -- celestial mechanics -- stars: individual: HR 8799.
© ESO 2009